1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
|
lz4(1) -- lz4, unlz4, lz4cat - Compress or decompress .lz4 files
================================================================
SYNOPSIS
--------
`lz4` [*OPTIONS*] [-|INPUT-FILE] <OUTPUT-FILE>
`unlz4` is equivalent to `lz4 -d`
`lz4cat` is equivalent to `lz4 -dcfm`
When writing scripts that need to decompress files,
it is recommended to always use the name `lz4` with appropriate arguments
(`lz4 -d` or `lz4 -dc`) instead of the names `unlz4` and `lz4cat`.
DESCRIPTION
-----------
`lz4` is an extremely fast lossless compression algorithm,
based on **byte-aligned LZ77** family of compression scheme.
`lz4` offers compression speeds of 400 MB/s per core, linearly scalable with
multi-core CPUs.
It features an extremely fast decoder, with speed in multiple GB/s per core,
typically reaching RAM speed limit on multi-core systems.
The native file format is the `.lz4` format.
### Difference between lz4 and gzip
`lz4` supports a command line syntax similar _but not identical_ to `gzip(1)`.
Differences are :
* `lz4` preserves original files
* `lz4` compresses a single file by default (use `-m` for multiple files)
* `lz4 file1 file2` means : compress file1 _into_ file2
* When no destination name is provided, compressed file name receives
a `.lz4` suffix
* When no destination name is provided, if `stdout` is _not_ the console,
it becomes the output (like a silent `-c`).
Therefore `lz4 file > /dev/null` will not create `file.lz4`
* `lz4 file` shows real-time statistics during compression
(use `-q` to silent them)
Default behaviors can be modified by opt-in commands, described below.
`lz4 -m` more closely follows `gzip` command line syntax,
supporting compression of multiple files into `.lz4`,
the last remaining difference being that source files are preserved by default.
Since it's also possible to erase source file using opt-in command `--rm`,
`lz4 -m --rm` behaves the same as `gzip`.
### Concatenation of .lz4 files
It is possible to concatenate `.lz4` files as is.
`lz4` will decompress such files as if they were a single `.lz4` file.
For example:
lz4 file1 > foo.lz4
lz4 file2 >> foo.lz4
then
lz4cat foo.lz4
is equivalent to :
cat file1 file2
OPTIONS
-------
### Short commands concatenation
In some cases, some options can be expressed using short command `-x`
or long command `--long-word`.
Short commands can be concatenated together.
For example, `-d -c` is equivalent to `-dc`.
Long commands cannot be concatenated.
They must be clearly separated by a space.
### Multiple commands
When multiple contradictory commands are issued on a same command line,
only the latest one will be applied.
### Operation mode
* `-z` `--compress`:
Compress.
This is the default operation mode when no operation mode option is
specified, no other operation mode is implied from the command name
(for example, `unlz4` implies `--decompress`),
nor from the input file name
(for example, a file extension `.lz4` implies `--decompress` by default).
`-z` can also be used to force compression of an already compressed
`.lz4` file.
* `-d` `--decompress` `--uncompress`:
Decompress.
`--decompress` is also the default operation when the input filename has an
`.lz4` extension.
* `-t` `--test`:
Test the integrity of compressed `.lz4` files.
The decompressed data is discarded.
No files are created nor removed.
* `-b#`:
Benchmark mode, using `#` compression level.
### Operation modifiers
* `-#`:
Compression level, with # being any value from 1 to 16.
Higher values trade compression speed for compression ratio.
Values above 16 are considered the same as 16.
Recommended values are 1 for fast compression (default),
and 9 for high compression.
Speed/compression trade-off will vary depending on data to compress.
Decompression speed remains fast at all settings.
* `-f` `--[no-]force`:
This option has several effects:
If the target file already exists, overwrite it without prompting.
When used with `--decompress` and `lz4` cannot recognize the type of
the source file, copy the source file as is to standard output.
This allows `lz4cat --force` to be used like `cat (1)` for files
that have not been compressed with `lz4`.
* `-c` `--stdout` `--to-stdout`:
Force write to standard output, even if it is the console.
* `-m` `--multiple`:
Multiple file names.
By default, the second filename is used as the destination filename
for the compressed file.
With `-m`, it is possible to specify any number of input filenames.
Each of them will be compressed independently, and the resulting name of
each compressed file will be `filename.lz4`.
This mode also reduces notification level.
* `-B#`:
Block size \[4-7\](default : 7)<br/>
`-B4`= 64KB ; `-B5`= 256KB ; `-B6`= 1MB ; `-B7`= 4MB
* `-BD`:
Block dependency (improves compression ratio on small blocks)
* `--[no-]frame-crc`:
Select frame checksum (default:enabled)
* `--[no-]content-size`:
Header includes original size (default:not present)<br/>
Note : this option can only be activated when the original size can be
determined, hence for a file. It won't work with unknown source size,
such as stdin or pipe.
* `--[no-]sparse`:
Sparse mode support (default:enabled on file, disabled on stdout)
* `-l`:
Use Legacy format (typically used for Linux Kernel compression)<br/>
Note : `-l` is not compatible with `-m` (`--multiple`)
### Other options
* `-v` `--verbose`:
Verbose mode
* `-q` `--quiet`:
Suppress warnings and real-time statistics; specify twice to suppress
errors too
* `-h` `-H` `--help`:
Display help/long help and exit
* `-V` `--version`:
Display Version number and exit
* `-k` `--keep`:
Don't delete source file.
This is default behavior anyway, so this option is just for compatibility
with `gzip(1)` / `xz(1)`.
### Benchmark mode
* `-b#`:
Benchmark file(s), using # compression level
* `-e#`:
Benchmark multiple compression levels, from b# to e# (included)
* `-i#`:
Minimum evaluation in seconds \[1-9\] (default : 3)
* `-r`:
Operate recursively on directories
BUGS
----
Report bugs at: https://github.com/lz4/lz4/issues
AUTHOR
------
Yann Collet
|
